KS-006

IMG_0984.JPG

Introduction
Enclosure
Crossover
Simulations
Measurements
Sound
Summary


Introduction

Original idea was to make a dipole speaker with single Jordan JX92 and two Peerless SLS-12" like this:
IMG_0970.JPG IMG_0971.JPG

Protype was done but JX92 was not behaving very well in open baffle. Small size, narrow gaps and transmission lines on the back side ruined polar and power responses.

Frequency response 0-180º
JX92-OB_FR_70cm_0-180deg_7ms_1p12oct.png
On-axis response(green) and 0-360º horizontal power average (red):
JX92-OB_FR_80cm_0+360deg-avg_7ms_1p12oct.png

This concept went to trash box even sound wasn't horrible. I require some objective qualities too.

Couple of years I've been thinking about symmetrical dipole without negative side effects of open baffle constructions. Now - with existing dipole woofer, it was good time to make symmetrical MT-section.

Technical specifications

General 3-way, dipole
Dimensions WW: 400 x 740 x 410 mm (W x H x D)
MT: 298 x 392 x 232 mm
X/O frequencies 250 Hz and 2.7 kHz
acoustically L-R2, mid inverted
Drivers Peerless SLS 12" 830669
Peerless HDS 5.25" Exclusive 831882
Seas 27TBCD/GB-DXT
Impedance 4/4/3 ohm


Enclosure

Enclosure drawing: KS-006.pdf

IMG_0979.JPG

IMG_0980.JPG IMG_0983.JPG

Crossover

DCX2496.


Measurements

Frequency response

In room at 230 cm, 5º
- time windows 4+400 ms, smoothing 1/6 oct.
KS-006_FR_230cm_5deg_4+400ms_1p6oct.png

Frequency response in room at 230 cm, 5º
- time window 5 ms, no smoothing (DFT)
KS-006_DFT_230cm_5deg_5ms_no-smooth.png
This includes floor and ceiling reflections.

Frequency response 0-90º, steps 15º
- measuring distance 80 cm, time window 7 ms, smoothing 1/12 oct.
KS-006-MT_FR_80cm_0-90deg-hor_7ms_1p12oct.png
Clear attenuation to 75...105º off-axis exists but polar response is spreaded.

On-axis response (green) and 0-360º horizontal power average (red) of MT-section
KS-006-MT_FR_80cm_0+360deg-hor-avg_7ms_1p12oct.png

On-axis response (black) and 0-360º horizontal+vertical power average (blue) of MT-section
KS-006-MT_FR_80cm_0-360deg-hor+ver-avg_7ms_1p12oct.png
5.25" cone is too small for dipole with baffle width of 298 mm. 4pi power average is close to omni-polar at 800-1200 Hz i.e. directivity index of ideal dipole is not reached.

Excess group delay

In room at 230 cm, 5º
KS-006_GDx_230cm_5deg_1p24oct.png
2nd order low passes keep delay quite low.

Step response

In room at 230cm, 5º
KS-006_SR_230cm_5deg.png

Burst decay

In room at 230cm, 5º
KS-006_BD_230cm_5deg.png
Room reflections increase energy at midrange...lower treble so much that  level of bass...lower midrange should be higher when only direct sound and floor reflection are included.

STI

In room at 230 cm, 5º
KS-006_STI_230cm_5deg.png
This is typical result for dipoles in our living room. Magnepans etc. reach higher values at midrange because of vertical directivity. Also conventional box speakers reach higher values because of higher directivity above midrange.

Impedance response

2xSLS-12"
SLS-12x2_dipole_ZR.png


Sound

Sound stage is deep, typically far behind speaker line. Good feature is that high frequencies are located close the same place with lower frequencies. There's not too much unnatural forwardness even with the worst recorded female voice. This requires reflections - diffused or mirror - from front wall, of course.

Resolution of midrange is quite low if listening distance is more than 240 cm. Trivial details are not available without heavy room treatment or very short listening distance. This may be ok for casual background listening but not my cup of tea.

Sensitivity and dynamics are not the highlight of this concept.

Dipole bass is quite ok, but lower bass with kick an authority is missing.


Summary

Midrange driver should be larger (compared to baffle) to avoid spreading of polar response. Bigger cone would also give more resolution at midrange because directivity index is maintained through upper midrange. Symmetrical MTM dipole with 4x 6.5" and tweeters with wave guide could be a good choice if vertical directivity is also needed.

Note! This was just R&D project. Do not use this design directly.

Page created 14.10.2011